PDS_VERSION_ID      = PDS3
RECORD_TYPE         = STREAM

OBJECT              = TEXT
 PUBLICATION_DATE   = 2007-05-25
 NOTE               = "Description of MARCI calibration process"
END_OBJECT          = TEXT
END


The following explanation of the MARCI calibration process assumes
0-relative indexing; e.g. the first pixel of any given line has
index 0.  File lines and dataset lines are also numbered starting
with 0.

There are eight input ancillary data files required for this process:
the decompanding table (marcidec.txt) and the per-band flattening
tables (vis1flat.ddd - vis5flat.ddd, uv6flat.ddd - uv7flat.ddd).
The decompanding table is a simple ASCII file; the flattening tables
are big-endian binary files.

0) Read the decompanding table file, marcidec.txt.  marcidec.txt
contains 256 lines, one line for each possible byte value [0, 255].
There is one value per line, namely the decompanded value
corresponding to the line number.

1) Read the flattening table file corresponding to the given MARCI
band.  The visible band flattening tables contain 16 1024-byte rows,
preceded by a 1024-byte header.  The UV flattening tables contain
2 128-floating point rows, preceded by a 1024-byte header.

The 1024-byte header has the following structure (big-endian):

0-rel byte offset   value
         0          32-bit integer magic number
         4          32-bit integer number of image lines
         8          32-bit integer number of bytes per image line
        12          32-bit integer number of bits per image elements
        16          32-bit integer currently unused
        20          32-bit integer currently unused
        24          ASCII label up to 1000 characters long
                    The label is NUL-terminated

The first word of the label contains the normalization factor for the
flattening table.  For UV flats, this factor is 1.; for VIS flats, we
currently have
                    201.66 norm band 1
                    211.30 norm band 2
                    202.42 norm band 3
                    198.74 norm band 4
                    208.89 norm band 5

2) Align the flattening table with the given MARCI band frame.  This
is only necessary when the visible band summing is not one; in this
case, the flattening table has to be averaged down so it has the same
width and height as the MARCI band frame.  For example, if the visible
band summing is 2, then the new flat has 8 512-element rows:

    new flat[i][j] = (flat[2i  ,2j] + flat[2i  ,2j+1]
                      flat[2i+1,2j] + flat[2i+1,2j+1])/4

3) Convert the flattening table to a numerator flat, e.g.,

    flat[i][j] = (flat[i][j] < 0.25) ? 0. : 1/flat[i][j]

4) For every frame for a given MARCI band, decompand the data and
apply the numerator flat:

    flattened value = raw decompanded value * numerator flat value

5) Convert the flattened data to radiance I/F using the following
formula:

   I = DN / Exposure Time / Summing / Response Coefficient

   F = Solar Irradiance / Pi / Solar Distance^2

   where DN is the flattened value

   Exposure Time is in milliseconds

   Solar Distance is in Astronomical Units (AU)

   # band   coeff     rms   solar_irradiance(1 AU)
     1      0.793     0.014    1798.4
     2      1.124     0.009    1875.7
     3      0.751     0.005    1742.7
     4      0.882     0.006    1580.7
     5      0.777     0.007    1360.3
     6      0.014     0.003    132.08
     7      0.033     0.003    755.64

   For UV band 7, summing should be multiplied by
   (1 - decimation_factor) when calculating I.
   decimation_factor = 0 for images acquired before
   2006-11-06T21:30:00 SCET and 0.75 for images acquired
   after that time.